1 files changed, 40 insertions, 1 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index dd06e18e5aac..e0913e469728 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -20,6 +20,7 @@
 #include <linux/buffer_head.h>
 #include <linux/blkdev.h>
 #include <linux/random.h>
+#include <linux/iocontext.h>
 #include <asm/div64.h>
 #include "compat.h"
 #include "ctree.h"
@@ -145,8 +146,9 @@ static noinline int run_scheduled_bios(struct btrfs_device *device)
         int again = 0;
         unsigned long num_run = 0;
         unsigned long limit;
+        unsigned long last_waited = 0;
 
-        bdi = device->bdev->bd_inode->i_mapping->backing_dev_info;
+        bdi = blk_get_backing_dev_info(device->bdev);
         fs_info = device->dev_root->fs_info;
         limit = btrfs_async_submit_limit(fs_info);
         limit = limit * 2 / 3;
@@ -207,7 +209,32 @@ loop_lock:
                 if (pending && bdi_write_congested(bdi) && num_run > 16 &&
                     fs_info->fs_devices->open_devices > 1) {
                         struct bio *old_head;
+                        struct io_context *ioc;
 
+                        ioc = current->io_context;
+
+                        /*
+                         * the main goal here is that we don't want to
+                         * block if we're going to be able to submit
+                         * more requests without blocking.
+                         *
+                         * This code does two great things, it pokes into
+                         * the elevator code from a filesystem _and_
+                         * it makes assumptions about how batching works.
+                         */
+                        if (ioc && ioc->nr_batch_requests > 0 &&
+                            time_before(jiffies, ioc->last_waited + HZ/50UL) &&
+                            (last_waited == 0 ||
+                             ioc->last_waited == last_waited)) {
+                                /*
+                                 * we want to go through our batch of
+                                 * requests and stop.  So, we copy out
+                                 * the ioc->last_waited time and test
+                                 * against it before looping
+                                 */
+                                last_waited = ioc->last_waited;
+                                continue;
+                        }
                         spin_lock(&device->io_lock);
 
                         old_head = device->pending_bios;
@@ -231,6 +258,18 @@ loop_lock:
         if (device->pending_bios)
                 goto loop_lock;
         spin_unlock(&device->io_lock);
+
+        /*
+         * IO has already been through a long path to get here.  Checksumming,
+         * async helper threads, perhaps compression.  We've done a pretty
+         * good job of collecting a batch of IO and should just unplug
+         * the device right away.
+         *
+         * This will help anyone who is waiting on the IO, they might have
+         * already unplugged, but managed to do so before the bio they
+         * cared about found its way down here.
+         */
+        blk_run_backing_dev(bdi, NULL);
 done:
         return 0;
 }